1. Field of the Invention
The present invention relates to an arrangement and to a method for the increase in the production of liquid natural gas and the conservation of energy and reduction of flash gas in a liquid natural gas manufacturing installation and, more particularly, relates to the reduction in the quantity of formed flash gas through the novel utilization of a hydraulic expander in the installation for extracting work from the flow of liquid natural gas prior to flashing thereof.
2. Discussion of the Prior Art
In liquid natural gas manufacturing facilities wherein liquid natural gas is conveyed from the manufacturing facility to a storage location subsequent to being flashed in a low pressure flash, a continuous stream of the liquid natural gas is conducted, as is well known in the technology, from the main exchanger of the liquid natural gas manufacturing facility through either a Joule-Thomson valve or a reversely operating pump which removes work from the flow, to a low-pressure flash in which the effluent from the Joule-Thomson valve or the reversely operating pump is divided into a first flow consisting of liquid natural gas which is conducted through the intermediary of a suitable transfer pump to a storage facility, and into a flow of natural gas vapor or flash gas which is adapted to be employed as fuel within the operating facility or plant.
Basically, the Joule-Thomson valve or reversely operating pump operate on the liquid natural gas stream flowing from the main exchanger of the liquid natural gas manufacturing facility at a very low temperature, thereby extensively reducing the temperature and pressure of the liquid flow, and wherein the extracted work using the reversely operating pump may be employed within the facility when converted into mechanical or electrical energy through suitable shaft-coupled compressors, pumps or generators in order to power other installation or plant components. Thus, the energy state change through the Joule-Thomson valve or the work recovered by the reversely operating pump, although relatively small in quantity, significantly enhances the production of liquid natural gas when flashed while producing a lower volume of flash gas or natural gas vapor, thereby improving the economical operation of the manufacturing facility. Although the utilization of Joule-Thomson valves and reversely operating pumps which extract work, such as centrifugal pumps or the like, in liquid gas manufacturing facilities result in an energy state change or the extraction of work from liquid streams under pressure, such as a cryogenic processing system for liquid natural gas which is conducted under high pressures and extremely low temperatures from the main exchanger of a liquid natural gas manufacturing facility, the energy state change or the work extracted has, generally, not been adequate to provide a degree of reduction in flash gas or natural gas vapor subsequent to flashing in a low pressure flash to a level of flash gas which will conform to the gas fuel requirements within the facility. Consequently, there is encountered an appreciable excess or waste of natural gases, with a concommitant reduction in the production of processed liquid natural gas, in which the economic production potential of the liquid natural gas manufacturing facility is not fully realized.